The present invention relates generally to communications and more particularly to systems and methods for wireless communications.
As the Internet continues its development and as workers and consumers increasingly rely on data networking to assist their day-to-day tasks, a need arises to extend network connectivity to locations where there is no convenient connection to a wired infrastructure. Workers desire to send and receive email and access the Internet and their corporate intranet even when they are away from their workstation. Consumers wish to establish home networks without costly and cumbersome wiring. Accordingly, wireless communication standards have evolved including the IEEE 802.11 family.
The current IEEE 802.11a standard allows for wireless communicates at speeds between 6 Mbps and 54 Mbps. It is desirable to further increase these speeds to accommodate delivery of multimedia wireless services and facilitate outdoor wireless bridging between indoor networks. It is also desirable to accommodate the increased data rates by increasing spectral efficiency rather than by increasing bandwidth.
One known way of increasing spectral efficiency is the use of MIMO (Multiple Input Multiple Output) processing techniques. MIMO techniques take advantage of multiple antennas (or multiple polarizations of the same antenna) at the transmitter and receiver to access multiple channel inputs and channel outputs and thereby define multiple spatial subchannels that occupy the same bandwidth but nonetheless are capable of carrying independent data streams. The delineation of the multiple spatial subchannels may involve weighting of the antenna inputs at the transmitter end and/or weighting of the antenna outputs at the receiver end. For further information on MIMO techniques, see U.S. Pat. No. 6,377,631.
It is desirable to apply MIMO techniques to IEEE 802.11 systems to increase data carrying capacity but there are obstacles to overcome. The 802.11 standards do not specify MIMO transmission techniques. It is desirable, and probably commercially essential, to construct wireless communication devices that cannot only interoperate with MIMO-capable devices but also with standards-defined devices that are not MIMO-capable. It is also desirable to modify the media access control (MAC) layer of standards such as the 802.11 standard to facilitate MIMO communications and allow 802.11 networks and other networks to benefit from increased capacity.